4. Erika & Rocket Game Center & Pokemon Tower
Well, Erika's battle was easy, probably the easiest battle in the whole game. Mono-Crobat can manage to finish the battle.
The rocket game center was a little bit harder than the Erika, but it's still not hard. I also evloved Charizard here. My pokemon easily got poison from Rocket's pokemon, I really need to get them back to pokemon center quite often.
My Current Team: Charizard, Pelipper, Archen, Jumpluff, Swoobat, Crobat
4.5 Planning before 5th Gym
The game allowed me to go to Saffron City or Fushcia City as my 5th Gym. Well, I thought the game assigned route should be Saffron City first as Sabrina's pokémon level was lower than that of Koga, but I needed to catch more pokemon first. So I designed ran down to Fuschia first along Route 16, 17 and 18. (I will also go back to Route 12-15 later.)
I knew I must get a gliscor and a skarmory for countering electric, ice and rock. At this moment, Jumpluff almost finished her main purpose to counter electric to 1x, and it should be replaced by gliscor. Jumpluff was also a little too weak right now with low attack and sp attack. But how about Skarmory?
Here, I decided to put Charizard into my box as I probably need it for my mono-fire run. (Refer to my rule for not using same Pokemon for Hall of Fame) To be honest, Charizard as Flying/Fire has little use for countering flying's weakness, but she should be more useful in mono-fire team as flying is 0x against ground attack.
Skarmory was caught in Route 18. Gligar was caught in Clear Forest (a new location at Route 15) and evolved by Razor fang to Gliscor.
My current team became as follows:
My Current Team: Pelipper, Archeops(evolved), Swoobat, Crobat, Skarmory, Gliscor
5. Koga
Before battling with Koga, I went through Route 12-15 to level up all my pokemon as well as had a look in Safari Zone. Well, Safari Zone got nothing really useful to me.

My main aim here was just gold teeth and HM03.
Koga's Gym was not difficult, except Koga. His pokemon was around lv45-48 (What!?) and his trainer was just around lv35. My pokemon here was just around lv40 which made me a harsh fight. My idea was using Swoobat and Gliscor to battle against his poison and… they are all fainted. And I used Skarmory as poison was 0x against steel and …. she got fainted.
!!!!!!!!!!!
Here, I gave my MVP to Archeops with ability Hustle. (Yes, the game changed her ability). I must say she was extremely powerful now with Hustle if I got luck for her accuracy. Hustle made her attack become extremely high and just an arcobatic can killed Koga's whole team.

Ok, anyway, I passed his challenge.
5.5 Planning, again (Be careful, it's a long long story.)
I got some problems with my team here, where Crobat seems to get nothing to do with her new team members Gliscor and Skarmory. Her speed was very high but… well, I must say, Poison/Flying was not a good offensive types here, and her attack was a little bit low compared to Archeops. Her defensive ability for both types and stats was also low compared to Gliscor and Skarmory. Other concern was I probably need her for mono-poison run for resisting ground attack (similar to that of Charizard).
I thought I may need to replace her to someone else, but… let me show some of my preference.
Charizard (again): I may take her out again, but I think my mono-fire need her more.
Zapdos: Zapdos can use up my Legendary place for mono-flying team. Actually Zapdos is a good choice for countering electric attack, but I still need to think my mono-electric run later, as electric team is extremely afraid of ground attack. If I use Zapdos here, I may need to use Emolga there. Oh, no.
Dragonite: Actually I think Dragonite was a good choice for countering electric. (I don't mind Ice as x2 and x4 made no difference actually, mostly just made the pokemon fainted directly.) And I don't think I need dragonite in mono-dragon later. But I already got a physical attacker Archeops in my team, another physical attacker Dragonite might not be the best choice here.
Altaria: Yes, it's a good choice besides dragonite as another Flying/Dragon. Wait, I can't use Mega as it lost flying type… If no mega-evolution, she was too weak…
Pinsir (Mega): Yes, Pinsir might be a good choice for mega evolution with bug/flying and ability aerilate. And her great attack stats can dominate my team… Wait, there's no Pinsirite in the game!?
OK, sorry but that's all what I think and consider. My thoughts had changed from Legendary to Mega-Evolution for finding a good flying pokemon with high sp attack… Wait, I found I missed out someone.
Pidgeot, with mega-evolution.
Mega Pidgeot actually fit what I want. A flying pokemon with high BST and high sp attack, and the most important, I absolutely don't need Mega Pidgeot for my other runs. Mega Evolution for Mono-normal run are probably Mega Kangaskhan or Mega Lopunny. Um… I never used Mega Pidgeot before even in online battle in previous generation. Maybe I should give her a try here.